Doesn't penance eliminate all Purgatory time?

The slight penances now given by priests during Confession are generally believed not to remit all purgatory time. During the ages of great faith, the Church used to give much more difficult penances to sinners. As a result of weakened faith, the Church has curtailed the use of more difficult penances in order not to discourage penitent sinners. The duty of expiating one's sins, however, still remains. Remember that there is a difference between receiving forgiveness of sins - which one does receive by the priest's absolution in Confession - and satisfying Divine Justice for sins committed. To put it in earthly terms, if someone vandalized your property, you may forgive the person yet still require the vandal to pay for the damage. Similarly, although God forgives an absolved sin, Divine Justice must still be satisfied.

How prayers help

When you pray for the poor souls, God applies the merits of your prayers towards those in Purgatory. The relief from prayers to the poor souls has been compared to the pouring of water on someone on fire. While prayers and partial indulgences may provide a measure of relief to the poor souls, a Plenary Indulgence makes it possible for a soul to be released immediately from Purgatory and enter heaven. The poor souls will always be grateful for your efforts on their behalf and will become your faithful friends for all eternity. (Note: Click here for information on indulgences.)

"In doing this he acted in a very excellent and noble way, inasmuch as he had the resurrection of the dead in view; for if he were not expecting the fallen to rise again, it would have been useless and foolish to pray for them in death. But if he did this with a view to the splendid reward that awaits those who had gone to rest in godliness, it was a holy and pious thought. Thus he made atonement for the dead that they might be freed from this sin." (2 Macc. 12:43-46) 

"Now, one of the easiest, yet one of the most powerful, means to procure relief for the souls in Purgatory is to say the beads [the Holy Rosary] for them with fervor. To say the Rosary for the souls in Purgatory is to offer up to God for their relief all the labors, fatigues, prayers, tears, contempt, sufferings, blood, and death - all the merits of the life of our dear Savior. Next to Mass, no more efficacious offering can be made to God then this for the relief of the souls in Purgatory." (Muller) 

To Gain a Plenary Indulgence

To gain a Plenary Indulgence from noon Nov. 1 until midnight Nov. 2, visit the church, pray for the Holy Souls and also for the intentions of the Holy Father.

On All Soul's Day and for a week afterward, a Plenary Indulgence for the Holy Souls is granted for a visit to the cemetery with devotion and prayer for the dead. All through November, you can gain partial indulgence every day you visit the cemetery and pray for the dead. Pleas see details below.

Plenary Indulgence

• For the Souls in Purgatory

A plenary indulgence, applicable only to the souls in purgatory, is granted each and every day from Nov 1 to Nov 8, who devoutly visit a cemetery and there pray, if only mentally, for the departed.

• For The faithful

A plenary indulgence is granted the faithful who, on All Souls’ Day (or according to the judgment of the bishop, on the Sunday preceding or following it, or on the solemnity of All Saints), devoutly visits a church or an oratory and recites an Our Father and the Creed.

Requirements for obtaining a plenary indulgence:

•  Do the work while in a state of grace,
•  Receive Sacramental confession within 20 days of the work (several plenary indulgences may be earned per reception),
•  Receive Eucharistic communion (one plenary indulgence may be earned per reception),
•  Pray for the pope’s intentions (Our Father and Hail Mary, or other appropriate prayer, is sufficient),
•  Have no attachment to sin (even venial) – i.e., it is sufficient that the Christian makes an act of the will to love God and despise sin.

Requirements for a partial indulgence:

• The work must be done while in a state of grace and with the general intention of earning an indulgence.

Notes:

• Only baptized persons in a state of grace who generally intend to do so may earn indulgences.
• Indulgences cannot be applied to the living, but only to the one doing the work or to the dead.
• Only one plenary indulgence per day can be earned (except for prayer at the hour of one’s own death).
• Several partial indulgences can be earned during the same day.
• If only part of a work with plenary indulgence attached is completed, a partial indulgence still obtains.
• If the penance assigned in confession has indulgences attached, the one work can satisfy both penance and indulgence.
• Confessors may commute the work or the conditions if the penitent cannot perform them due to legitimate obstacles.
• In groups, indulgenced prayer must be recited by at least one member while the others at least mentally follow the prayer.
• If speech/hearing impairments make recitation impossible, mental expression or reading of the prayer is sufficient.
• For an indulgence attached to a particular day requiring a church visit, the day begins at noon the day before and ends at midnight.

(Source from:http://acatholiclife.blogspot.com.au/2016/11/all-souls-day.html)